Preheat your oven to 350°F.,Make the filling: In a medium bowl, combine the melted butter and maple syrup. Whisk in the brown sugar, cornmeal, and kosher salt.,______,Slowly pour the egg mixture into the maple mixture and whisk just until combined.,Place the blind-baked shell on a parchment-lined baking sheet. Brush the crimped edge with the beaten egg. Pour the maple filling into the pie shell until it reaches the bottom of the crimps.,Transfer the baking sheet with the pie on it to the oven and bake for 45 minutes to 1 hour, until the edges are puffed and the center jiggles only slightly when shaken. It will continue to set as it cools.,Remove the baking sheet from the oven and transfer the pie to a wire rack to cool for 4 to 6 hours. Once fully cooled and at room temperature, sprinkle generously with flaky sea salt, slice into 6 to 8 pieces, and serve.,Store leftover pie, well wrapped in plastic wrap or under a pie dome, at room temperature for up to 3 days.,In a large stainless steel bowl, combine the flour, sugar, and salt and stir to mix well. Place the sticks of butter in the bowl and coat on all sides with the flour mixture. Using a bench scraper, cut the butter into 1/2-inch cubes. Work quickly to separate the cubes with your hands until they are all lightly coated in flour. Grab that bench scraper once again and cut each cube in half. I always tell my pie dough students that it's unnecessary to actually cut each cube perfectly in half, but it's a good idea to break up the butter enough so that you can be super-efficient when it's pastry blender time.,It's pastry blender time! Switch to the pastry blender and begin to cut in the butter with one hand while turning the bowl with the other. It's important not to aim for the same spot at the bottom of the bowl with each stroke of the pastry blender, but to actually slice through butter every time to maximize efficiency. When the pastry blender clogs up, carefully clean it out with your fingers (watch out, it bites!) or a butter knife and use your hands to toss the ingredients a bit. Continue to blend and turn until the largest pieces are the size and shape of peas and the rest of the mixture feels and looks freakishly similar to canned Parmesan cheese.,At this point, add the water-vinegar mixture all at once, and switch back to the bench scraper. Scrape as much of the mixture as you can from one side of the bowl to the other, until you can't see visible pools of liquid anymore. Now it's hand time. Scoop up as much of the mixture as you can, and use the tips of your fingers (and a whole lot of pressure) to press it back down onto the rest of the ingredients. Rotate the bowl a quarter-turn and repeat. Scoop, press, and turn. With each fold, your intention is to be quickly forming the mixture into one cohesive mass. Remember to incorporate any dry, floury bits that have congregated at the bottom of the bowl, and once those are completely gone and the dough is formed, it's time to stop.,Remove the dough from the bowl, place it on a lightly floured counter, and use your bench scraper to divide it into two equal pieces. Gently pat each into a 2-inch-thick disc, working quickly to seal any broken edges before wrapping them tightly in a double layer of plastic wrap. If you're portioning for a lattice-topped pie, shape one half into a 2-inch-thick disc and the other half into a 6 by 3-inch rectangle. Refrigerate the dough for at least 2 hours or, ideally, overnight. When you go to roll out the crust, you want the discs to feel as hard and cold as the butter did when you removed it from the fridge to make the dough. This will make the roll-out way easier.,You can keep the pie dough in the fridge for a few days or in the freezer for up to 1 year. If frozen, remove the dough and place it in the refrigerator to thaw one full day before you intend to use it. If you're planning to make only one single-crust pie, wrap the discs separately and place one in the freezer.,NOTE: Icy water, now improved and with tang: While working at Brooklyn's Four & Twenty Blackbirds for a summer, I learned a number of good tricks that considerably changed my pie dough-making experience. Here's one of my favorites: Fill a 1-cup liquid measuring cup with about 1 inch of water and freeze until completely frozen. Just after you mix your dry ingredients, grab it from the freezer and fill with water plus 2 tablespoons or so of apple cider vinegar. The ice-cold water-vinegar mixture should look just like apple juice. Let it chill on your counter while you mix the other ingredients for the dough.,NOTE 2: The addition of vinegar to pie dough was originally thought to tenderize the gluten (thus avoiding a tough crust), but there isn't any good scientific evidence proving that it makes a difference. We keep it in our recipe for its tangy flavor and our respect for tradition.,NOTE 3: Not the pie-baking plan-ahead type? That's okay! When you're ready to make the dough, simply fill a 1-cup liquid measuring cup about halfway with ice, then add water and 2 tablespoons apple cider vinegar.